Fan Doesn’t Run
FAN DOESN’T RUN – The indoor blower motor does not come on and there is no cold air coming out of the registers.
If the outdoor unit is running and there is no air being delivered by the indoor blower, it will only take a matter of minutes for the indoor coil to “freeze-up”. You should turn the system “Off” and contact a qualified service technician.
In some cases, the indoor coil being frozen prevents air from coming out of the registers, making it appear that the blower is not operating. If the indoor coil or connecting lines are frozen and you can hear the blower operating, see FREEZING-UP.
POSSIBLE PROBLEM & DESCRIPTION
Thermostat Set Incorrectly
Many “No cool” calls (especially early season) are the result of the thermostat being set incorrectly. Make sure the thermostat “System” switch is set to “Cool” (or “Auto” for auto-change-over thermostats) and the cooling temperature is set lower than the current space temperature.
Loss of Power to the Furnace or Air Handler
Low voltage power for the thermostat and controls comes from the furnace. Make sure there is high voltage power to the furnace or air handler. Make sure breakers and any service disconnects are turned on.
Most newer furnaces are equipped with a blower door safety switch the "kills" power when the blower door is removed. Make sure the blower door is securely in place.
An unlikely, but possible, cause is a bad thermostat. Try turning the Fan switch to the "On" position to see if the blower comes on. Watch the video. If the blower operates in the "On" position and does not operate when the air conditioner is running, you may have a bad thermostat.
Bad Blower Motor - Qualified Technician Recommended
If the blower motor does not start when the air conditioner comes on (no air blowing out of the registers), it could be the result of a bad blower motor.
One diagnostic step that can be taken is to turn the fan to the “On” position at the thermostat. If the fan operates, this would indicate that the problem is most likely something other than the fan motor. It may be necessary to leave the fan in the "On" position so the A/C can continue to operate until the problem is resolved.
If the fan does not operate automatically on a call for cooling, or after turning the thermostat fan switch to the "On" position, this may indicate either a bad blower motor or a bad capacitor (below).
A failed blower motor will often be accompanied by a bad odor (like burning plastic or rubber).
Bad Capacitor - Qualified Technician Recommended
Most direct-drive PSC fan motors require a capacitor which provides extra power for starting.
A fan motor with a bad capacitor will typically attempt to start but will fail while making a louder-than-normal humming noise.
After several seconds of humming, the motor will typically overheat and shut-off and then retry after about 30-60 seconds of cooling.
Sometimes a motor will still be able to start (with difficulty) with a bad capacitor.
A fan motor that runs normally after helping to start by turning by hand usually indicates a bad capacitor.
Control Board - Qualified Technician Recommended
Most newer gas furnaces and air handlers use a computerized control board to activate the blower motor during a cooling cycle. The control board should start the blower motor immediately on a call for cooling.
Some older gas furnaces use a belt-drive blower motor. If the belt becomes extremely loose or breaks, the blower wheel will not turn even though the motor is operating.